Toddler sleep

Hi, 2 and a half year old daughter keeps waking up in the night and wanting one of us, usually her mom. We have to go into her and wait with her till she falls asleep. She can sometimes do this 3-4 times a night, sometimes she wakes up and opens her door and comes into our room. We straight away take her back to her room but have to stay with her till she falls asleep. If we try and leave before she is asleep then she just sits on her bed screaming. When we first but her down for bed again we have to wait with her till she falls asleep. She has always slept through apart ftom this last few months were she has started to do this. How do we get back to her sleeping through and not waking and wanting us, we are so tired.